Method for operating a traction drive automatic transmission for automotive vehicles

ABSTRACT

A method for operating an automatic traction drive transmission for use in motor vehicles having a first gear unit for operation in an infinitely variable mode and a second gear unit for operation in a continuously variable mode includes connecting the first gear unit to the transmission output, disconnecting the second gear unit from the first gear unit, and changing the speed ratio of the variator to produce low forward and low reverse ranges, or connecting the second gear unit to the first gear unit, disconnecting the first gear unit from the transmission output, and changing the speed ratio of the variator to produce high mode low and high forward ranges.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of automatic transmissionsfor motor vehicles. More particularly it pertains to a method foroperating such a transmission having a traction drive variator of thetoroidal type.

2. Description of the Prior Art

One type of a continuously variable transmission typically includes atoroidal drive having at least one pair of traction discs, which oftenreact upon each other and are rotatably supported in a housing along anaxis facing one another to define a toric cavity between them. A motiontransmitting traction roller is disposed in the cavity. The tractionroller is frictionally engaged with the discs in circles of varyingdiameters depending on the transmission ratio, and is so supportive thatit can be moved to initiate a change in the transmission ratio. Atraction drive continuously variable drive can have more than one cavityand may be used, for example, to form part of an infinitely variabletransmission.

A common type of continuously variable transmission includes a toroidaldrive having dual cavities, which are defined by two torsionally coupledoutboard traction discs, which react upon each other, and two inboarddiscs, which are positioned between the outboard discs and also reactupon each other. One dual cavity toroidal drive of the "off-center type"is disclosed in U.S. Pat. No. 5,368,529. An off-center toroidal drive isusually considered to have an included angle of less than 180 degreebetween the traction contacts, i.e., where the roller contacts thediscs. An on-center toroidal drive is usually considered to have anincluded angle of about 180 degree. The included angle is the angleformed by the lines between the center of the toric cavity and thetraction contact on the engaged discs. The usual method for transmittingpower through a dual cavity design of the "off-center type" is to inputthe power to the two outboard discs and use parallel shafting andgearing to transmit power from the inboard discs.

One gear mesh used to effect this parallel shafting is usually trappedbetween the inboard discs. Such a two-shaft system is bulky anddifficult, if not impossible, to fit into the available space providedfor the transmission of a number of vehicles. In addition, it is oftennecessary to return to the original center line when transmitting power.In the past, this has required a second gear mesh to be used, inaddition to the gear mesh between the inboard discs. Single cavitytoroidal drives are also known to take up more space than desired.

Therefore, there is a need for a toroidal type transmission capable ofinputting and outputting power along the same axis without having to useparallel shafting. U.S. Pat. No. 5,607,372 describes an axialtransmission of this type. Such a coaxial-axial drive transmission takesup less space than parallel shaft transmissions and can therefore beused in applications with tighter space constraints. In addition, it iseasier and less expensive to package a coaxial-axial drive transmissionin a housing than to package a parallel shaft transmission.

Transmissions of this type in the prior art do not have enough speedratio span to overdrive the variator output. Instead, in infinitelyvariable transmissions of this type, upon shifting from a low mode to ahigh mode, the speed ratio produced by the variator is reduced and thetransmission speed ratio increases as a result of the increase in thespeed ratio of the gearset. To reduce the variator speed ratio therollers are rotated to the low mode configuration from the higher speedratio configuration to which they had progressed while accelerating thevehicle from a stop.

Transmissions operating in this way are difficult to controleffectively. It is preferred that the variator speed ratio increasecontinually when the gearset is shifted to a higher speed range withoutbeing decreased to a low mode of operation.

SUMMARY OF THE INVENTION

One feature of the transmission controlled by the method of thisinvention is a planetary gearset having a carrier connected to thetransmission input, and a sun gear connected to the output of a tractiondrive. The traction drive is a toroidal drive having two coupledtraction discs, which react at least torsionally, preferably bothtorsionally and axially, with one another through the carrier. Thetoroidal drive can be a dual cavity type, with two outboard tractiondiscs and one inboard traction disc element or two separate inboardtraction discs disposed between the outboard discs. The toroidal drivecan also be a single cavity type. One of the traction discs rotates withthe input shaft; the carrier rotates with the input shaft and the othertraction disc.

It is an object of this invention to provide a coaxial traction drivetransmission that operates in an infinitely variable mode including ageared neutral condition and in a continuously variable mode. It isanother object to provide such a transmission in which transmissionspeed ratios are increased by progressively increasing the speed ratiosproduced by the variator as the motor vehicle accelerates from a stop.In accomplishing this result, the variator underdrives its output discsas the vehicle accelerates from a stop and continually increases thevariator speed ratios into the overdrive range without decreasing thevariator speed ratio, even upon changing the operating mode of thetransmission at the synchronous point where the torque flow path changesby alternately engaging and disengaging two clutches that control thegearsets.

In realizing these objects and advantages a method for operating atraction drive transmission, having a traction drive variator driveablyconnected to a transmission input, a first gear unit driveably connectedto the transmission input and variator output, a second gear unitdriveably connected to the first gear unit, includes the steps ofdriveably connecting the first gear unit and the transmission output;operating the variator to overdrive the variator output with respect tothe speed of the transmission input such that the transmission outputdrives the vehicle in a rearward direction; and operating the variatorto underdrive the variator output with respect to the speed of thetransmission input such that the transmission output drives the vehiclein a forward direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a traction drive transmission accordingto this invention.

FIG. 2 is a friction element application chart showing the engaged anddisengaged status of the clutches that correspond to each of theoperating ranges of the transmission of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a transmission according to this invention includesan input shaft 10 driven by an internal combustion engine, electricmotor or other power source, and including a planetary gearset 12, acompound planetary gearset 14, a toroidal traction drive variator 16,various elements driveably connecting components of the gearsets andvariator, and an output shaft 18.

Toroidal variator 16 includes first input discs 20, driveably connecteddirectly to the input shaft 10, and second input discs 22, driveablyconnected to shaft 10 and the carrier 24 of the planetary gearset 12.The variator output discs 26 are driveably connected through a sleeveshaft 28 to a first sun gear 30 of gearset 12. The variator discs aremutually spaced axially and define toroidal cavities 36, 38, each cavitycontaining a set of spaced, rotating, angularly displaceable rollers 32,34, each roller set driveably engaged with an input disc and outputdisc. Rollers of the set 32 transmit torque between input discs 20 andoutput discs 26; rollers of the set 34 transmit torque between inputdiscs 22 and the output discs 26 A drive ratio control mechanism tiltsor inclines the axes of the rollers through arcs, thereby changing thelocation of contact of the rollers on the discs, the speed of the outputdisc relative to the speed of the input discs, and the torquetransmitted between the input discs and output discs. Output discs 26rotate in the opposite direction from that of the input discs about theaxis of input shaft 10.

The dual cavity toroidal drive 16 includes two inboard traction discs 26formed as one integral element mounted on shaft 28. However, inboarddiscs 26 can also be two separate discs which are positionedback-to-back and simply coupled together in a conventional manner tooperate in unison. An example of a dual cavity toroidal drive havingdual inboard discs is disclosed in U.S. Pat. No. 5,368,529, which isincorporated in its entirety herein by reference.

A toric cavity is defined between each outboard disc 20 and 22 and theinboard disc element 26. Each pair of traction rollers 32, 34 are mirrorimages of the other pair. The rollers are so supported that they can bemoved to produce a change in the transmission ratio.

Each roller is actuated to vary its diameter and to provide a normalforce at its contact with the corresponding discs to sufficientlysupport the traction forces needed to effect a change in speed ratio.The outboard discs 20 and 22 impinge on the traction rollers, causingthe traction rollers to rotate. As they rotate, the traction rollersimpinge on and rotate the inboard disc element 26 in a directionopposite to that of the rotating outboard discs.

In addition to first sun gear 30, the first epicyclic gearset 12includes a second sun gear 40; a ring gear 42; a long planet pinion 44in continuous meshing engagement with sun gears 30 and 40; a second setof planet pinions 46 in continuous meshing engagement with ring gear 42and planet pinion 44; and a carrier 24 driveably connected to inputshaft 10 and output disc set 22 for rotatably supporting the planetpinion sets 44 and 46.

The second compound planetary gearset 14 includes a sun gear 48; ringgear 50 surrounding the sun gear 48; a set of planet pinions 52continually meshing with sun gear 48; a second set of planet pinions 54in continuous meshing engagement with ring gear 50 and planet pinion set52; and a carrier 56 driveably connected to output shaft 18 forrotatably supporting the planet pinions of sets 52 and 54. Ring gear iscontinually fixed to the transmission housing, and carrier 56 is fixedto output shaft 18.

The operation of gearsets 12 and 14 is controlled by a first clutch 60,adapted to alternately driveably connect carrier 56 and ring gear 42when the clutch is engaged and to release that connection by disengagingclutch 60. A second clutch 62 is adapted alternately to driveablyconnect sun gear 40 and sun gear 48 by engaging the clutch and torelease that connection when the clutch is disengaged.

Throughout this description, reference is made to preferred gear andpinion sizes and to preferred overdrive and underdrive speed ratiosproduced by variator 16. In a preferred embodiment of this invention,sun gears 30, 40 have 81 teeth, ring gear 42 has 199 teeth, and planetpinions 46, 44 each have 56 teeth. With regard to the components ofgearset 14 in the preferred application, sun gear 48 has 47 teeth, ringgear 50 has 105 teeth, and each of the planet pinions 52, 54 has 26teeth.

The transmission is capable of operating in a geared neutral conditionwith clutch 60 engaged and clutch 62 disengaged. In order to produce thegeared neutral condition for the preferred embodiment, the roller sets32, 34 of variator 16 are arranged angularly within the toroidalcavities 36, 38 such that the speed of output discs 26 is approximately-1.457 times the speed of input shaft 10. This corresponds to a variatorspeed ratio of 1.457. The variator speed ratio is defined as theabsolute value of the ratio of the speed of the output discs 26 to thespeed of the input shaft 10. Sun gear 30 is driven at the speed of discs26, carrier 24 is driven directly from input discs 20, 22 at the samespeed as that of input shaft 10 and the output is taken at ring gear 42.With the transmission so disposed, the speed of ring gear 42, carrier 56and output shaft 18 is substantially zero.

The vehicle accelerates or drives away in the forward direction from thegeared neutral condition by changing the drive ratio of variator 16 tothe low mode forward ratio. A low mode forward range, having an overallspeed ratio of about 0.40, is produced by setting the angular positionof rollers 32, 34 such that they contact variator discs 26 at a radiallyouter position and contact variator input discs 20, 22 at radially innerposition, the opposite configuration from that showing in FIG. 1. In lowmode forward, discs 26 and sun gear 30 are driven at approximately -0.47times the speed of input shaft 10, and carrier 24 is driven at the speedof shaft 10. With clutch 60 engaged, ring gear 42 drives carrier 56 andoutput shaft 18 through clutch 60 at approximately 0.402 times the speedof shaft 10.

The vehicle accelerates from stop while the transmission continues tooperate in the low mode forward condition, i.e., with clutch 60 engagedand clutch 62 disengaged. A synchronous point occurs when the rotationalspeeds of the components connected by clutch 62, sun gears 40 and 48,are substantially equal, and the speed of the components connected byclutch 60, carrier 56 and ring gear 42, are substantially equal. At thesynchronous point, clutch 62 is engaged and clutch 60 is disengaged,thereby placing the transmission in the high mode low condition.

During a transition from the low mode forward mode to the synchronouspoint, the angular inclination of rollers 32, 34 is maintainedsubstantially constant, and the output variator discs 26 are driven atapproximately -0.470 times the speed of input shaft 10.

The transmission operates in the forward high mode high condition withclutch 62 engaged and clutch 60 disengaged. In the high mode highcondition, the angular inclination of rollers 32, 34 is changedgradually from the underdrive position described above with reference tothe low mode forward and high mode low conditions to the overdriveposition shown in FIG. 1 where the rollers 32, 34 contact the inputdiscs 20, 22 at radially outer positions and contact the output variatordiscs 26 at radially inner positions. As the variator changes in thisway from the underdrive to the overdrive positions, carrier 24 is drivenat the speed of shaft 10 through variator input discs 20, 22 and sungear 30 is driven directly from variator output discs 26 in a preferablerange from approximately -0.470 to -2.120 times the speed of input shaft10. The speed and torque of sun gear 30 is transferred through pinionset 44 to sun gear 40, which drives sun gear 48, due to the engagementof clutch 62, at the same speed as that of sun gears 30, 40. Ring gear50 continually provides a torque reaction due to its engagement with thetransmission housing. With variator 16 at the maximum overdriveposition, the transmission output shaft 18 is driven by carrier 56 ofgearset 14 at approximately 1.718 times the speed of the input shaft.

The transmission of FIG. 1 can operate in a low mode reverse conditionupon disengaging clutch 62, engaging clutch 60, and adjusting thevariator to operate in the overdrive condition, i.e., with the rollers32, 34 generally in the position shown in FIG. 1. With the variator sodisposed, sun gear 30 is driven at approximately -2.12 times the speedof input shaft 10, ring gear 50 provides the torque reaction, and theoutput is taken at ring gear 42, which drives carrier 56 and outputshaft 18 at approximately -0.270 times the speed of input shaft 10, inthe preferred embodiment.

Although the form of the invention shown and described here constitutesthe preferred embodiment of the invention, it is not intended toillustrate all possible forms of the invention. Words used here arewords of description rather than of limitation. Various changes in theform of the invention may be made without departing from the spirit andscope of the invention as disclosed.

We claim:
 1. A method for controlling operation of a transmission of a motor vehicle, the transmission having a traction drive variator driveably connected to a transmission input, a first epicyclic gear unit driveably connected to the transmission input and variator output, a second epicyclic gear unit, the method comprising the steps of:driveably connecting the first epicyclic gear unit and the transmission output; driveably disconnecting the first epicyclic gear unit from the second epicyclic gear unit; operating the variator to overdrive the variator output with respect to the speed of the transmission input such that the transmission output drives the vehicle in a rearward direction; and operating the variator to underdrive the variator output with respect to the speed of the transmission input such that the transmission output drives the vehicle in a forward direction.
 2. The method of claim 1, further comprising:operating the transmission in a geared neutral condition by operating the variator to overdrive the variator output with respect to the speed of the transmission input such that the transmission output speed is substantially zero.
 3. The method of claim 1, further comprising:driveably disconnecting the first epicyclic gear unit and transmission output when the variator produces synchronous speed; driveably connecting the second epicyclic gear unit and a component of the first epicyclic gear unit when the variator produces synchronous speed; and operating the variator to overdrive the variator output with respect to the speed of the transmission input such that the transmission output drives the vehicle in the forward direction.
 4. A method for controlling operation of a transmission for a motor vehicle, the transmission having a traction drive variator driveably connected to a transmission input, a first epicyclic gear unit driveably connected to the transmission input and variator output for driving the transmission output in an infinitely variable operating mode, a second epicyclic gear unit adapted for drive connection to the first gear unit for driving the transmission output in a continuously variable operating mode, the method step comprising the steps of:driveably connecting the first epicyclic gear unit and the transmission output and disconnecting the first epicyclic gear unit from the epicyclic second gear unit; operating the variator to overdrive the variator output at a first speed ratio relative to speed of the transmission input such that the transmission output drives the vehicle in a rearward direction; and operating the variator to underdrive the variator output at a second speed ratio less that the first speed ratio such that the transmission output drives the vehicle in a forward direction.
 5. The method of claim 4, further comprising:operating the transmission in a geared neutral condition by operating the variator to overdrive the variator output at a third speed ratio whose magnitude is less than the first speed ratio and greater than the second speed ratio such that the transmission output speed is substantially zero.
 6. The method of claim 4, further comprising:driveably connecting the second epicyclic gear unit and a component of the first epicyclic gear unit; driveably disconnecting the first epicyclic gear unit and the transmission output; operating the variator to overdrive the variator output such that the transmission output drives the vehicle in the forward direction.
 7. The method of claim 6, further comprising:increasing the overdrive speed ratio of the variator such that the speed of the variator output is in a range bounded by the first speed ratio and second speed ratio, and the vehicle is driven in a forward direction. 